System was connected to network router at least for two weeks. It decided to clean up all UPnP mappings and I2P router now thinks that there is no UPnP devices around, but at ​http://127.0.0.1:7657/netdb?r=. it still thinks it is reachable. I2P router should recheck UPnP mappings regulary, because any user on the internal network can drop these mappings.